The present invention relates to a masking sound generator and, more particularly, to a multi-channel masking sound generator which provides multiple channels of masking sound signals which are matched in spectrum although incoherently related within the spectrum.
As is known in the art, see for example U.S. Pat. Nos. 4,059,726 and 3,980,827, it is advantageous, in the generation of a masking sound field, that the signals from adjacent loudspeakers should not be coherently related within the masking spectrum since coherency causes disturbing variations in local intensity due to cancellation and reinforcement effects. Accordingly, it is increasingly recognized as good practice to provide multiple signals which are incoherently related as to frequencies within the masking spectrum. Such signals may, for example, be provided by means of a multiple output random noise generator of the type disclosed in copending, co-assigned U.S. Ser. No. 303,496.
It is also understood in the art, however, that it is typically necessary to tailor the electrical power spectrum applied to the loudspeakers in order to produce the desired acoustic spectrum within the environment in which the masking field is to be applied. Further, this tailoring of the spectrum must typically be adjusted or fit to each specific application since the sound absorbing characteristics of walls and furniture within the environment will typically vary from one situation to the next. Similiarly the frequency responses of different types of loud speakers will also vary from situation to situation. As will be understood by those skilled in the art, it can be a difficult and time-consuming procedure to adjust each filter set so as to empirically obtain a desired acoustic spectrum within a given environment. Further, the difficulty is greatly compounded if multiple channels, each containing its own filter set, must be separately adjusted and tailored to yield the same acoustic spectrum.
Among the objects of the present invention may be noted a provision of a novel multi-channel masking sound generator; the provision of such a generator which facilitates the matching of spectrums between several channels provided by the generator; the provision of such a generator which provides multiple channels which are matched in spectrum but which are incoherently related for frequencies within the spectrum; the provision of such a generator which is easily adjusted; the provision of such a generator which is highly stable and reliable and which is of relatively inexpensive and simple construction. Other objects and features will be in part apparent and in part pointed out hereinafter.